Effects of settling pond sediments on the Bonsall Creek Estuary: a preliminary study

The Crofton Pulp and Paper Mill operates a settling pond for a water treatment plant that clarifies water diverted from the Cowichan River. The pond requires flushing of accumulated contents into the Bonsall Creek estuary. In recent years, approximately 885 t y super(-1) of sediment has been diverted from the Cowichan River to the Bonsall Creek estuary resulting in excessive sedimentation of gel-mud sediment on between 2.0 and 7.2 ha of mudflat. Anomalous patterns of sediment composition in the intertidal zone as well as visual observations by local citizens have raised concerns about potential effects on the estuarine ecosystem. The distribution and abundance of epibenthic and infaunal organisms, plant communities, and sediment size distributions were assessed in the estuary May 19-20 1998. This report summarizes the survey results and presents a preliminary analysis of the potential effects of the gel-mud from the settling pond outfall on the estuary fauna and flora.